Gear indexing woes

[Kbrook]

I have just replaced my chainset through choice not because its worn out, and its done 10,000+ miles, cassettes well depends on level even 105 cassettes can be had for £22-23 and Ultegra 6700 for £30, I would expect 6000 miles from a cassette minimum of 3,000 from a chain, £60 a year on chains £40-60 on cassettes hardly expensive, but as I say depends on level of kit.
Look at what is happening, its changing up but not down as if something is holding it back or the spring isn't strong enough, to me thats extra friction somewhere that the return spring can not over come.

Agree with this.

I checked rear mech, whilst that would affect shifting that wouldnt be specific to changing to smaller cogs. Its a cable/ cable outer issue.

 

[Nigelnaturist]

Like I said I have just changed the front chainset and from start to finish including resetting up the FD (height and angle) maybe 2hrs this included fitting the chainrings pedals ect works like a dream whats more its a 26/38/50 triple, the rear when I set that was maybe 10 mins to adjust cable tension and position ( I hate the term re-indexing, because it not really what you are doing, the indexing is controlled by the shifters and can not be changed), any time the RD doesn't shift down is usually after bad weather when road crud has got on to the cable then in to the outer or on the bottom cable guide and exactly the same thing happens changes up but not down so well, a little dip it the road and it will then shift down on its own as momentarily the tension is broken.
This doesn't tend to happen these days as I change my cables and outers 1-2 times a year.

 

[JoeyB]

We fixed this in the end.

The main culprit was the outer cable. As soon as that was replaced there was an instant improvement in gear change. He also replaced the rear cassette for good measure but the improvement came before that was fitted.

 

[snorri]

Ditch the derailleur and fit hub gears if you don't want to be constantly tinkering.

 

[Nigelnaturist]

Ditch the derailleur and fit hub gears if you don't want to be constantly tinkering.

This problem could occur with any cable gear system.

 

[JoeyB]

Tinkering is part of the fun...forget hub gears - fixed or go home lol

 

[snorri]

Tinkering is part of the fun.

Not for everyone.

 

[KneesUp]

I had the same problem which was fixed yesterday, it was drivingnme nuts, I had changed my chain, cassette, checked the hanger, even changed the cable to the rear derailleur. Every time it would change up fine but not down. In the end I took it to the LBS who took five minutes to change the cable outers. Sorted straight away. He explained that when you go up the block the pressure of the lever is enough to tighten the cable, but any **** in the outer will prevent a proper release of the spring in the RD.

I bet you have the same issue.

Or like me you could have changed the cable outers and accidentally used brake cable for one section of the run (it was late, ok?) which compresses, unlike gear cable. My gear rear cable has outer from the bar ends to the top tube, then runs naked to the seat post where there is some outer to angle it down to the rear stays. It is then bare cable again until the loop at the dérailleur. The 15cm bit near the seatpost is brake cable. I've decided that's why it won't work - it's exactly the same as the OPs - pretty good going up, and rubbish going down. You can't even go one gear at a time in friction mode. (And I've replaced the rear dérailleur tonight so it's not that - the jockey wheels on the old one were shocking so I was blaming that, even though it had only started being a problem since I did the cables, and a new Acera mechanism was only a few quid more than jockey wheels for the rather worn Altus one that was on.)